In an apparatus for working a material, usually referred to as an extruder, the extruder may be of the type wherein twin co or counter rotating non-intermeshing screws are disposed within a barrel bore. The extruder is generally divided into sections or zones for the performance of different operations. For example, there is a feed section wherein material fed into the extruder is conveyed into a second section which may be a mixing section or a section wherein a reaction takes place. Sectioning is generally achieved, especially in those instances which require zones of differing pressures, by the placement of flow restriction means between the zones. Many tinges, it is necessary to have the reaction section under a positive pressure in order to promote the reaction of materials. Thereafter, the reacted materials are then passed to an area of lower pressure wherein undesirable liquids and volatiles are released from the reaction mixture. The construct of the extruder is such that between the barrel bores, wherein the screws are placed, there is a channel or opening which may function as a conduit for the undesired liquids.
One way in which the pressure is maintained in the reaction section is to have a flow restriction means on each screw between the high pressure zone and a low pressure zone. The material being treated will flow against this restriction means thereby creating substantial back pressure. The magnitude of this back pressure determines the pressure differential between the upstream high pressure zone and the downstream low pressure zone. Unfortunately, because of the channel between the barrel bores, there is considerable pressure leakage between the high pressure zone and the low pressure zone. This leakage diminishes the capacity of the restrictions on the screws to maintain a pressure differential between the high and low pressure zones.
This pressure leakage results in the material in the high pressure zone being at a pressure which is not as great as desired. In some reactions, conducted within a high pressure zone, because of the pressure leakage from the high pressure zone to the low pressure zone, raw material usage is greatly increased to obtain the amount of product which would have been obtained if the pressure in the high pressure zone could have been maintained at a constant higher level.
U.S. Pat. No. 2,615,199 discloses a means for obtaining a high pressure when working a material in an extruder. However, U.S. Pat. No. 2,615,199 fails to teach or suggest any means for preventing loss of pressure between a high pressure area and a low pressure area due to the channels between the barrel bores. These channels are generally referred to as the "nip" or "apex" between the barrel bores. In general, it is standard that the distance from one barrel bore center to the other barrel bore center is equal to the diameter of the barrel bore itself.
It is an object of this invention therefore to provide a means for maintaining a high back pressure in a non-intermeshing parallel or tangential co or counter rotating twin screw extruder.
Another object of this invention is to provide a process for processing material at a high pressure wherein pressure loss from a high pressure zone to an adjacent zone of lower pressure, is minimized.
Still another object of this invention is to provide a device which allows for the continuous adjustment of a pressure drop over a flow restricting means in a non-intermeshing, co or counter rotating twin screw extruder.
A further object of this invention is to provide a device which will enable the operator to establish a higher pressure drop between adjacent extruder zones than may be achieved in conventional barrel sections.
Other objects and advantages will become apparent from the following more complete description and claims.